The present invention has to do with the testing and/or analyzing of fluid mixtures flowing through fluid conducting lines and is particularly concerned with an improved apparatus that is particularly suited for analyzing and determining the net volumes of oil, gas and water of production fluid flowing from oil wells.
The present invention has to do with certain notable improvements in that apparatus for testing and analyzing fluid mixtures that is the subject matter of and that is fully disclosed in my earlier issued U.S. Pat. No. 3,911,256, issued Oct. 7, 1975. The full disclosure of U.S. Pat. No. 3,911,256 is incorporated herein by reference and will hereinafter be referred to as the patent.
To the best of my knowledge and belief, the patent is the most pertinent prior art and was representative of the state of the art at the time of my present invention.
In the patent the need for determining the net oil content of the production fluids issuing from oil wells is fully and clearly set forth.
The patent also describes that old method and apparatus employed to test oil well production fluids to determine the net oil content thereof that was, and remains, the most common and widely used method and apparatus for determining the net oil content of oil well production fluid throughout the petroleum industry at the time of the invention of the patent apparatus. That old and common method and apparatus for testing production fluid is characterized by the provision and use of three-phase separator tanks in and through which production fluids issuing from oil wells are caused to flow at a sufficiently slow rate to allow the force of gravity to cause free water in the production fluid to settle to the bottoms of the tanks, for the lighter oils to rise to the top of the settled water and for free gases to rise in the tanks above the oil. The volumes of separated water, gas and oil in the tanks are measured and recorded and samples of the separated oil (wet oil) are extracted from the tanks and tested to determine the net volumes of the water, gas and oil fractions thereof.
In the apparatus of the referred-to patent, the use of a three-phase separator tank is eliminated and in its stead the apparatus includes an elongate vertical test chamber that is filled with and holds a sample of production fluid to be tested. That apparatus operates to read and record the flow rate, temperature, pressure and weight of the sample of fluid in the chamber and operates to alter the pressure on the sample in the chamber to expand or compress the gas in the chamber and to vary the volume of the sample in the course of calculating and determining the net gas content of the sample. The net oil and/or net water content of the sample is determined by subtracting the measured volume and weight of the gas from the total volume and weight of the sample to determine the net volume and weight of the remaining water and oil in the sample and comparing the measured volume and weight of the water and oil with base or reference measurements of the volume and weight earlier obtained from a prepared anhydrous sample of the oil. The net volume of oil in the sample being tested is established by subtracting the measured weight thereof from the measured weight of a like volume of anhydrous oil.
The apparatus of the referenced patent has proven to be effective to test and determine the net oil content of oil well production fluid containing oil that has a specific gravity that is notably different from the specific gravity of water. As the specific gravity of oil in production fluid tested nears the specific gravity of water, the difficulty and time required to calculate and determine the net content of oil increases at an exponential rate and the accuracy and dependability of the apparatus diminishes in a like manner. That apparatus is rendered totally ineffective when the specific gravity of the oil is the same as water. In practice, the apparatus of the referred-to patent cannot reliably and dependably analyze oil well production fluid containing oil the API gravity of which is between 14 and 7 degrees API. Accordingly, the apparatus of my referred-to patent is not suitable for use in analyzing oil well production fluids containing those heavy crude oils that characterize the production from most oil deposits throughout the world.
In addition to the foregoing, the apparatus which is the subject matter of my above referred-to patent has proven to be such that it requires closer monitoring and field service than many of those who own, maintain and service oil field production equipment are willing to be burdened with. This is due to the fact that the apparatus includes many mechanical parts that are subject to leaking and failing and that must be periodically serviced, repaired and/or replaced. For example, the patented apparatus includes the flow meter, four large fall valves, a double-acting hydraulic cylinder and piston unit and link means for operating those valves; a source of motive hydraulic fluid and an electrically operated four-way valve for controlling operation of the cylinder and piston unit; a motor-driven high-pressure liquid pump with a related check valve and an electrically operated plug valve for introducing and removing liquid from the test chamber. It is an accepted rule-of-thumb that the likelihood of mechanical failure in such apparati increases exponentially with the number of mechanical parts included.